05000315/LER-2025-002, Supplemental Diesel Generators (DG) Unavailable Resulting in Emergency DGs Inoperable Greater than Allowed by TS
| ML25302A454 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 10/29/2025 |
| From: | Dailey S Indiana Michigan Power Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| AEP-NRC-2025-40 LER 2025-002-00 | |
| Download: ML25302A454 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3152025002R00 - NRC Website | |
text
An MP Company BOUNDLESS ENERGY° Indiana Michigan Power Cook Nuclear Plant One Cook Place Bridgman, Ml 49106 indianamichiganpower.com October 29, 2025 AEP-NRC-2025-40 10 CFR 50.73 Docket Nos.: 50-315 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Unit 1 LICENSEE EVENT REPORT 315/2025-002-00 Supplemental Diesel Generators (SDGs) Unavailable Resulting In Emergency Diesel Generators (EDGs) Inoperable Greater Than Allowed By Technical Specification In accordance with 10 CFR 50. 73, Licensee Event Report (LER) System, Indiana Michigan Power Company, the licensee for Donald C. Cook Nuclear Plant Unit 1, is submitting as an enclosure to this letter the following report:
LER 315/2025-002-00: Supplemental Diesel Generators (SDGs) Unavailable Resulting In Emergency Diesel Generators (EDGs) Inoperable Greater Than Allowed By Technical Specification There are no commitments contained in this submittal.
Should you have any questions, please contact Mr. Michael K. Scarpello, Regulatory Affairs Director, at (269) 466-2649.
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Site Vice President OAF/sjh
Enclosure:
Licensee Event Report 315/2025-002-00: Supplemental Diesel Generators (SDGs)
Unavailable Resulting In Emergency Diesel Generators (EDGs) Inoperable Greater Than Allowed By Technical Specification
U.S. Nuclear Regulatory Commission Page2 c:
EGLE - RMD/RPS J. B. Giessner - NRC Region Ill NRC Resident Inspector N. Quilico - MPSC R. M. Sistevaris - AEP Ft. Wayne S. P. Wall, NRC Washington D.C.
A. J. Williamson - AEP Ft. Wayne AEP-NRC-2025-40
Enclosure to AEP-NRC-2025-40 Licensee Event Report 315/2025-002-00: Supplemental Diesel Generators (SDGs)
Unavailable Resulting In Emergency Diesel Generators (EDGs) Inoperable Greater Than Allowed By Technical Specification
NRCFORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04130/2027 (04--02-2024)
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- 1. Faclllty Name
~ 050
- 2. Docket Number
"* r-aga Donald C. Cook Nuclear Plant Unit 1 052 315 1 OF 3
- 4. Title Supplemental Diesel Generators (DG) Unavailable Resulting in Emergency DGs Inoperable Greater Than Allowed by TS
- 5. Evant Data
- 6. LER Number
- 7. Report Data
- 8. Other Facllltlaa Involved Month Day Year Year Sequentlal Rnlalon Month Day Year Faclllty Name Docket Number Number No.
050 09 03 2025 2025 -
002 -
00 10 29 2025 FacllltyName Docket Number 052
- 9. Operating Mode 1 O. Power Leval 1
100
)
1111... usuac1 \Limn 10 1 "'"' spaces, 1.e., approx1ma191y 1;, srng1e-spaceu,ypewnaen 11nes1 On September 3, 2025, with Unit 1 in Mode 1 at 100% power, it was identified that the calculation for the required fuel oil volume for both Supplemental Diesel Generators (SDG1)[DG] and (SDG2)[DG]) had been revised to account for vortexing in the fuel oil tanks [TK]. This revision resulted in a higher required minimum fuel oil volume to support 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of SDG operation at 55% load. As a result, the SDGs are considered unavailable whenever their associated fuel oil tank level falls below the revised minimum fuel oil volume of 3450 gallons.
During review of the SDG fuel oil tank levels for the previous three years two instances were identified where the volume was less than 3450 gallons while being credited for entry into the Technical Specification Action Statement (TSAS) 3.8.1.B.5 which requires restoration of the required Emergency Diesel Generator (EDG)[DG] to OPERABLE status within 14 days.
The direct cause was a failure to include consideration for unusable volume due to vortexing in the calculation for SDG minimum fuel oil volume calculation. The Technical Requirements Manual has been revised with the updated minimum fuel oil volume for both SDGs. The identified condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a Condition Prohibited by Technical Specifications.
EVENT DESCRIPTION
~
EsUmated
- 2. DOCKET NUMBER
'I I CD UIIUDCI 00315 I
YEAR SEQUENTIAL I
NUMBER 2025 - II 002 I -II REV NO.
oo __ J On September 3, 2025, with Unit 1 in Mode 1 at 100% power, it was identified that the calculation for the required fuel oil volume for both Supplemental Diesel Generators (SDG1 )[DG] and (SDG2)[DG] had been revised to account for vortexing in the fuel oil tanks [TK]. This revision resulted in a higher required minimum fuel oil volume to support 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of SDG operation at 55% load. As a result, the SDGs are considered unavailable whenever their associated fuel oil tank level falls below the revised minimum fuel oil volume of 3450 gallons.
Unit 1 Limiting Condition of Operation 3.8.1 requires two EDGs capable of supplying the onsite Class 1 E power distribution subsystem(s) to be OPERABLE in MODE 1. If one EOG becomes inoperable and either SDG is unavailable then the Completion Time is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to restore both SDGs to available status or restore the required EOG to Operable.
With this COMPLETION TIME not met the affected Unit is required to be in MODE 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, in MODE 5 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
During a review of the SDG fuel oil tank levels for the previous three years two instances were identified where the volume was less than 3450 gallons while being credited for entry into Technical Specification Action Statement (TSAS) 3.8.1.B.5 which requires restoration of the required Emergency Diesel Generator (EDG)[DG] to OPERABLE status within 14 days.
In the period from February 26, 2023, at 01 :00 to March 2, 2023, at 20: 18, totaling 115.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, the 1 CD EOG was INOPERABLE for maintenance. At the same period of time SDG1 fuel oil tank level was 3327 gallons and SDG2 fuel oil tank level was 3326 gallons resulting in unavailability with these volumes of fuel oil. It was determined that at the lowest noted fuel oil volume, an SDG would operate for 23.24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
From June 8, 2025, at 00:01 until June 12, 2025, at 23:57, totaling 120.0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />, the 1 AB EOG was INOPERABLE for maintenance. At the same period of time SDG1 fuel oil tank level was 3392 gallons and SDG2 fuel oil tank level was 3380 gallons resulting in unavailability with these volumes of fuel oil. It was determined that at the lowest noted fuel oil volume, an SDG would operate for 23.46 hours5.324074e-4 days <br />0.0128 hours <br />7.60582e-5 weeks <br />1.7503e-5 months <br />.
The SDGs were unavailable when TSAS 3.8.1.B.5 was entered on both occurrences and therefore the identified condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a Condition prohibited by Technical Specifications.
COMPONENT 1-OME-150-AB 1-OME-150-CD 12-OME-250-SDG1 12-OME-250-SDG2
CAUSE OF THE EVENT
The direct cause is the calculation did not account for vortexing. Revising the calculation to account for vortexing resulted in more fuel required in each SDG fuel oil tank than the unrevised TRM value of 2200 gallons.
As a result the,SDGs were unavailable any time their associated fuel oil volume was less than the revised value of 3450 gallons.
NUCLEAR SAFETY I
- 2. DOCKET NUMBER 3 LERNUMBER I
YEAR SEQUENTIAL REV 00315 NUMBER NO.
2025. I 002 1-0 A probabilistic risk assessment (PRA) was performed to estimate the impact, of the two occurrences where an EOG was inoperable longer than allowed by Technical Specification due to SDG unavailability, on Core Damage Frequency (CDF) and Large Early Release Frequency (LERF).
The evaluation performed resulted in an estimated change of CDF and LERF that is within the bounds for Very Low Safety Significance" as described within NRC Inspection Manual Chapter 0609.
INDUSTRIAL SAFETY There was no actual or potential industrial safety hazard resulting from this event.
RADIOLOGICAL SAFETY There was no actual or potential radiological safety hazard resulting from this event.
CORRECTIVE ACTIONS
CORRECTIVE ACTIONS TAKEN Site procedures were revised to ensure minimum fuel oil tank level is maintained greater than or equal to 3450 gallons for each SDG.
The TRM for both units were revised to specify each SDG fuel oil tank contains greater than or equal to 3450 gallons of fuel oil.
PLANNED CORRECTIVE ACTIONS
None
PREVIOUS SIMILAR EVENTS
Review of Licensee Event Reports for the past five years found no events due to similar causes. Page 3
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